The battery system used in a conventional all-electric or hybrid vehicle is required to store large amounts of energy within the confines of a relatively small battery enclosure. In addition to housing tens to thousands of individual cells in order to meet the power requirements of such a vehicle, this type of battery pack must be capable of surviving the inherent thermal and mechanical stresses of a car for a period of years. Additionally, while the housing used to package a multi-cell vehicle battery must be structurally sound enough to allow battery pack inspection and/or replacement, it must do so with minimal weight since hybrids and electric cars are exceptionally sensitive to excess weight. The design of such a vehicle battery pack should also lend itself to efficient, and preferably automated, manufacturing practices.
In addition to the various packaging constraints placed on the battery pack, it is also imperative that the batteries be protected from any event that may lead to one or more of the cells within the pack entering into thermal runaway, thermal runaway occurring when the internal reaction rate increases to the point that more heat is being generated than can be withdrawn. Thermal runaway may be initiated by a short circuit within the cell, improper cell use, physical abuse, manufacturing defects, or exposure of the cell to extreme external temperatures. Given that a thermal runaway event can lead to significant property damage and, in some circumstances, bodily harm or loss of life, the battery systems used in most all-electric or hybrid vehicles employ one or more means of preventing, detecting and mitigating the effects of such an event.
While there are a variety of systems and techniques that may be used to protect the batteries with a vehicle's battery pack as well as the vehicle's occupants during normal vehicle use, it will be appreciated that a vehicle collision presents an extremely difficult challenge given the limited control afforded by such an event. Due to the energy densities and voltages/currents associated with such battery systems, in addition to thermal event containment, during a severe collision it is imperative that the high voltage battery pack be decoupled from the vehicle's electrical system. In such a situation decoupling the battery pack is critical to insuring the safety of the vehicle's occupants as they leave the vehicle, first responders attempting to aid the occupants or control the event, and mechanics/technicians attempting to mitigate potential vehicle damage as well as initiate vehicle repairs.
In a conventional all-electric or hybrid vehicle, inertial switch sensors are commonly used to decouple the battery pack from the electrical system during a crash. Such sensors, however, operate over a relatively large range of g-forces (e.g., 10-35 g's). Additionally, such sensors are relatively insensitive to directionality and are not capable of being programmed to respond differently to different types of events. Accordingly, what is needed is a means of safely and consistently disconnecting the high voltage system in the event of a crash. The present invention provides such a system.